This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-307608, filed Oct. 3, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of electropolishing a metallic material.
2. Description of the Related Art
A metal burying wiring technology is utilized in the manufacture of a semiconductor device. In forming a buried metallic wiring layer, an insulating film is formed first on a semiconductor substrate, followed by forming a wiring groove of a prescribed pattern within the insulating film. A barrier layer is formed on the inner surface of the wiring groove and on the surface of the insulating film. Then, a metallic wiring material is deposited, filling the wiring groove and covering the barrier layer portion formed on the surface of the insulating film. Further, a portion of the metallic wiring material other than that portion of the metallic wiring material that is present inside the wiring groove is subjected to an electropolishing. The electropolishing is performed until the surface of the barrier layer formed on the surface of the insulating film is exposed. After the electropolishing step, the barrier metal on the surface of the insulating film is removed by a chemical mechanical polishing (CMP) technology. It is advantageous to carry out the electropolishing treatment by applying a voltage across an anode electrode and a counter electrode while bringing the anode electrode into contact with the surface of the metallic wiring material (material subjected to the electropolishing) within the electrolytic solution.
It has been customary to use platinum as the anode electrode in the electropolishing referred to above. It has been found, however, that oxygen tends to be generated on the platinum anode electrode in subjecting a wiring material made of a noble metal such as ruthenium to an electropolishing by using the platinum anode electrode. If oxygen is generated on the platinum anode electrode during the electropolishing, electricity is consumed, resulting in failure to dissolve the noble metal wiring material.
The oxygen generation is not the problem encountered only when the platinum anode electrode and the noble metal wiring material are used in combination. In general, oxygen is generated when the reductant such as OHxe2x88x92 within the electrolytic solution is brought into contact with the surface of an anode electrode so as to deprive the anode electrode of an electron and, thus, to be converted into an oxidant such as O2. As a result, the current efficiency is lowered during the electropolishing treatment.
What should also be noted is that, in the ordinary electropolishing treatment, the electric field is not stabilized during the electropolishing treatment because of the diffusion of the electrolytic solution, the generation of hydrogen on the counter electrode, and the difference in the intensity of the electric field between the central portion and the edge portion of the counter electrode. As a result, a local electropolishing is generated in the material subjected to the electropolishing treatment.
According to a first aspect of the present invention, there is provided an electropolishing method, comprising applying a voltage across an anode electrode and a counter electrode within an electrolytic solution while bringing the anode electrode into contact with a surface of a target material, thereby electropolishing the target material, wherein the anode electrode is formed of an electrode material having a current density not higher than 10 mA/cm2 upon application of a voltage of +2.5V vs. silver/silver chloride electrode within a 0.1 M perchloric acid solution in an electrochemical measurement using a potentiostat.
According to a second aspect of the present invention, there is provided an electropolishing method, comprising applying a voltage across an anode electrode and a counter electrode within an electrolytic solution while bringing the anode electrode into contact with a surface of a target material, thereby electropolishing the target material, wherein the anode electrode has an insulating film provided on a side surface thereof.
Further, according to a third aspect of the present invention, there is provided an electropolishing method, comprising applying a voltage across an anode electrode and a counter electrode within an electrolytic solution while bringing the anode electrode into contact with a surface of a target material, thereby electropolishing the target material, wherein the counter electrode has a solid electrolyte film, an ion exchange resin film or a resistivity film formed on a surface thereof.